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                                                                  Exhibit 10(aa)

                    POTASH CORPORATION OF SASKATCHEWAN INC.
                  STOCK OPTION PLAN -- OFFICERS AND EMPLOYEES

1.   PURPOSE OF PLAN

     Potash Corporation of Saskatchewan Inc. (the "Corporation") by resolution
     of its Board of Directors (the "Board") has established this Plan to
     encourage officers and employees of the Corporation and its subsidiaries to
     promote the growth and profitability of the Corporation by providing them
     with the opportunity through options to acquire Common Shares of the
     Corporation ("Common Shares").

2.   ADMINISTRATION

     This Plan shall be administered by the Board.

3.   GRANT OF OPTIONS

     From time to time the Board may designate individual officers and employees
     of the Corporation and its subsidiaries eligible to be granted options to
     purchase Common Shares and the number of Common Shares which each such
     person will be granted an option to purchase; provided that the aggregate
     number of Common Shares subject to such options may not exceed the number
     provided for in paragraph 4 of this Plan.

4.   SHARES SUBJECT TO OPTION

     The aggregate number of Common Shares issuable after February 3, 1998
     pursuant to options under this Plan may not exceed 6,926,125 shares. The
     number of Common Shares issuable pursuant to options under this Plan shall
     be subject to adjustment under paragraphs 8 and 9.

     The aggregate number of Common Shares in respect of which options have been
     granted to any one person and which remain outstanding shall not at any
     time exceed 5% of the number of issued and outstanding Common Shares (on a
     non-diluted basis) at that time.

     If any option granted under this Plan, or any portion thereof, expires or
     terminates for any reason without having been exercised in full, the Common
     Shares with respect to which such option has not been exercised shall again
     be available for further options under this Plan.

5.   OPTION PRICE

     The option price under this Plan to any optionee shall be fixed by the
     Board when the option is granted and shall be not less than the fair market
     value of the Common Shares at such time which, for optionees resident in
     the United States and any other optionees designated by the Board, shall be
     deemed to be the closing price per share of the Common Shares on the New
     York Stock Exchange on the last trading day immediately preceding the day
     the option is granted and, for all other optionees, shall be deemed to be
     the closing price per share of the Common Shares on The Toronto Stock
     Exchange on the last trading day immediately preceding the day the option
     is granted; provided that, in either case, if the Common Shares did not
     trade on such exchange on such day the option price shall be the closing
     price per share on such exchange on the last day on which the Common Shares
     traded on such exchange prior to the day the option is granted.

6.   TERMS OF OPTION

     The period during which an option is exercisable may not exceed 10 years
     from the date the option is granted, and the option agreement may contain
     provisions limiting the number of Common Shares with
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     respect to which the option may be exercised in any one year. Each option
     agreement shall contain provisions to the effect that:

     a.    if the employment of an optionee as an officer or employee of the
           Corporation or a subsidiary terminates, by reason of his or her
           death, or if an optionee who is a retiree pursuant to clause b below
           dies, the legal personal representatives of the optionee will be
           entitled to exercise any unexercised options, including such options
           that may vest after the date of death, during the period ending at
           the end of the twelfth calendar month following the calendar month in
           which the optionee dies, failing which exercise the options
           terminate;

     b.    subject to the terms of clause a above, if the employment of an
           optionee as an officer or employee of the Corporation or a subsidiary
           terminates, by reason of retirement in accordance with the then
           prevailing retirement policy of the Corporation or subsidiary, the
           optionee will be entitled to exercise any unexercised options,
           including such options as may vest after the date of retirement,
           until the expiry date of such options or the date on which such
           options are otherwise terminated in accordance with the provisions of
           this Plan, failing which exercise the options terminate.
           Notwithstanding the foregoing, the Board may, at the time of grant,
           prescribe such shorter period of time for exercise following
           retirement as it deems appropriate;

     c.    if the employment of an optionee as an officer or employee of the
           Corporation or a subsidiary terminates, for any reason other than as
           provided in the preceding clauses a or b, the optionee will be
           entitled to exercise any unexercised options, to the extent
           exercisable at the date of such event, during the period ending at
           the end of the calendar month immediately following the calendar
           month in which the event occurs, failing which exercise the options
           terminate.

           For greater certainty and for these purposes, an optionee's
           employment with the Corporation or a subsidiary shall be considered
           to have terminated effective on the last day of the optionee's actual
           and active employment with the Corporation or subsidiary whether such
           day is selected by agreement with the optionee or unilaterally by the
           Corporation or subsidiary and whether with or without advance notice
           to the optionee. For the avoidance of doubt, no period of notice that
           is given or ought to have been given under applicable law in respect
           of such termination of employment will be utilized in determining an
           optionee's entitlement under the Plan; and

     d.    each option is personal to the optionee and is not assignable, except
           (i) as provided in the preceding clause a, and (ii) at the election
           of the Board, an option may be assignable to the spouse, children and
           grandchildren of the original optionee and to a trust, partnership or
           limited liability company, the entire beneficial interest of which is
           held by one or more of the foregoing.

    Nothing contained in the preceding clauses a, b, or c shall extend the
    period during which an option may be exercised beyond its stipulated expiry
    date or the date on which it is otherwise terminated in accordance with the
    provisions of this Plan.

    If an option is assigned pursuant to the preceding subclause (ii) of clause
    d, the references in the preceding clauses a, b and c to the termination of
    employment or death of an optionee shall not relate to the assignee of an
    option but shall relate to the original optionee. In the event of such
    assignment, legal personal representatives of the original optionee shall
    not be entitled to exercise the assigned option, but the assignee of the
    option or the legal personal representatives of the assignee may exercise
    the option during the applicable specified period.

7.  EXERCISE OF OPTIONS

    Subject to the provisions of this Plan, an option may be exercised from time
    to time by delivering to the Corporation at its registered office a written
    notice of exercise specifying the number of shares with respect to which the
    option is being exercised and accompanied by payment in cash or certified
    cheque in full of the purchase price of the shares then being purchased.
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8.  ADJUSTMENTS

    Appropriate adjustments to the authorized limits set forth in paragraph 4,
    in the number, class and/or type of shares optioned and in the option price
    per share, both as to options granted or to be granted, may be made by the
    Board in its discretion to give effect to adjustments in the number of
    Common Shares which result from subdivisions, consolidations or
    reclassifications of the Common Shares, the payment of share dividends by
    the Corporation, the reconstruction, reorganization or recapitalization of
    the Corporation or other relevant changes in the capital of the Corporation.
    If the Corporation sells all or substantially all of its assets as an
    entirety or substantially as an entirety, options under this Plan may be
    exercised, in whole or in part, at any time up to and including (but not
    after) a date 30 days following the date of completion of such sales or
    prior to the close of business on the date the option expires, whichever is
    earlier.

9.  MERGERS

    If the Corporation proposes to amalgamate or merge with another body
    corporate, the Corporation shall give written notice thereof to optionees in
    sufficient time to enable them to exercise outstanding options, to the
    extent they are otherwise exercisable by their terms, prior to the effective
    date of such amalgamation or merger if they so elect. The Corporation shall
    use its best efforts to provide for the reservation and issuance by the
    amalgamated or continuing corporation of an appropriate number of shares,
    with appropriate adjustments, so as to give effect to the continuance of the
    options to the extent reasonably practicable. In the event that the Board
    determines in good faith that such continuance is not in the circumstances
    practicable, it may upon 30 days' notice to optionees terminate the options.

10. CHANGE OF CONTROL

    If a "change of control" of the Corporation occurs, each then outstanding
    option granted under this Plan may be exercised, in whole or in part, even
    if such option is not otherwise exercisable by its terms. For purposes of
    this paragraph 10, a change of control of the Corporation shall be deemed to
    have occurred if:

     a.    within any period of two consecutive years, individuals who at the
           beginning of such period constituted the Board and any new directors
           whose appointment by the Board or nomination for election by
           shareholders of the Corporation was approved by a vote of at least a
           majority of the directors then still in office who either were
           directors at the beginning of the period or whose appointment or
           nomination for election was previously so approved, cease for any
           reason to constitute a majority of the Board;

     b.    there occurs an amalgamation, merger, consolidation, wind-up,
           reorganization or restructuring of the Corporation with or into any
           other entity, or a similar event or series of such events, other than
           any such event or series of events which results in securities of the
           surviving or consolidated corporation representing 50% or more of the
           combined voting power of the surviving or consolidated corporation's
           then outstanding securities entitled to vote in the election of
           directors of the surviving or consolidated corporation being
           beneficially owned, directly or indirectly, by the persons who were
           the holders of the Corporation's outstanding securities entitled to
           vote in the election of directors of the Corporation prior to such
           event or series of events in substantially the same proportions as
           their ownership immediately prior to such event of the Corporation's
           then outstanding securities entitled to vote in the election of
           directors of the Corporation;

     c.    50% or more of the fixed assets (based on book value as shown on the
           most recent available audited annual or unaudited quarterly
           consolidated financial statements) of the Corporation are sold or
           otherwise disposed of (by liquidation, dissolution, dividend or
           otherwise) in one transaction or series of transactions within any
           twelve month period;

     d.    any party, including persons acting jointly or in concert with that
           party, becomes (through a take-over bid or otherwise) the beneficial
           owner, directly or indirectly, of securities of the Corporation
           representing 20% or more of the combined voting power of the
           Corporation's then outstanding
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           securities entitled to vote in the election of directors of the
           Corporation, unless in any particular situation the Board determines
           in advance of such event that such event shall not constitute a
           change of control; or

     e.    the Board approves and/or recommends that shareholders accept,
           approve or adopt any transaction that would constitute a change of
           control under clause b, c or d above.

11. AMENDMENT OR DISCONTINUANCE OF THIS PLAN

    The Board may amend or discontinue the Plan at any time but, subject to
    paragraphs 8, 9, and 10, no such amendment may increase the aggregate
    maximum number of shares that may be subject to option under this Plan,
    change the manner of determining the minimum option price, extend the option
    period under any option beyond 10 years or, without the consent of the
    holder of the option, alter or impair any option previously granted to an
    optionee under this Plan. Amendments to the Plan require pre-clearance of
    The Toronto Stock Exchange.

12. EVIDENCE OF OPTIONS

    Each option granted under this Plan shall be embodied in a written option
    agreement between the Corporation and the optionee which shall give effect
    to the provisions of this Plan.